Power amplifier module

ABSTRACT

A power amplifier module includes an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.

This is a continuation of U.S. patent application Ser. No. 15/380,383 filed on Dec. 15, 2016 which is a continuation of U.S. patent application Ser. No. 15/077,124 filed on Mar. 22, 2016 which claims priority from Japanese Patent Application No. 2015-070089 filed on Mar. 30, 2015. The contents of these applications are incorporated herein by reference in their entireties.

BACKGROUND

The present disclosure relates to a power amplifier module.

In mobile communication devices, such as cellular phones, a power amplifier module for amplifying power of a signal to be transmitted to a base station is used. Nowadays, in cellular phones, modulation methods using standards for high-speed data communication, such as HSUPA (High-Speed Uplink Packet Access), LTE (Long Term Evolution), and LTE-Advanced, are being used. In these communication standards, for enhancing the communication speed, it is desirable to decrease a phase deviation and an amplitude deviation. Accordingly, it is necessary that a power amplifier module implement high linearity. In the above-described communication standards, for achieving the enhanced communication speed, the range in which the amplitude of a signal changes (dynamic range) is usually wide. For maintaining high linearity even in the case of a wide dynamic range, a high power supply voltage is necessary, and this is likely to increase the power consumption in a power amplifier module.

On the other hand, in cellular phones, for increasing the maximum talk time or the maximum communication time, it is desirable to decrease the power consumption. For example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-513943 discloses a power amplifier module utilizing the envelope tracking technique. In the envelope tracking technique, by adjusting the power supply voltage in accordance with the amplitude level of an input modulation signal, the power efficiency is improved.

BRIEF SUMMARY

Envelope tracking is effective particularly for enhancing power-added efficiency when a power amplifier is operating under high power. On the other hand, when a power amplifier is operating under low power, another technique, such as average power tracking, is sometimes used for improving the linearity of the gain.

Generally, a power amplifier module includes a bias circuit for supplying bias to a power amplifier transistor. The bias circuit includes a transistor at its base to which a bias control voltage is supplied and a ballast resistor connected to the emitter of the transistor. A suitable value of the bias control voltage and a suitable resistance value of the ballast resistor of a power amplifier module vary in accordance with the operation mode and the output level of the power amplifier module. It is thus difficult to provide the optimal bias circuit adjusted to all operation modes.

The present disclosure has been made in view of such a background. Accordingly, the present disclosure suitably controls bias to be supplied to an amplifier transistor in a power amplifier module that is operable in multiple operation modes.

According to embodiments of the present disclosure, there is provided a power amplifier module including an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.

According to embodiments of the present disclosure, it is possible to suitably control bias to be supplied to an amplifier transistor in a power amplifier module that is operable in multiple operation modes.

Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of embodiments of the present disclosure with reference to the attached drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates an example of the configuration of a transmitting unit including a power amplifier module, which is an embodiment of the present disclosure;

FIG. 2 illustrates an example of the configuration of a power amplifier module;

FIG. 3 illustrates an example of the configuration of bias circuits;

FIG. 4A is a graph illustrating an example of the relationship between the output level (dBm) and the power-added efficiency (%) when a power amplifier module is operating in the envelope tracking (ET) mode;

FIG. 4B is a graph illustrating an example of the relationship between the output level (dBm) and the gain (dB) when a power amplifier module is operating in the average power tracking (APT) mode;

FIG. 5 illustrates an example of the configuration of a bias circuit when an amplifier transistor is a multi-finger transistor;

FIG. 6 illustrates another example of the configuration of the bias circuit when the amplifier transistor is a multi-finger transistor;

FIG. 7 illustrates an example of the configuration of the bias circuit;

FIG. 8 illustrates another example of the configuration of the bias circuit;

FIG. 9 illustrates another example of the configuration of the bias circuit when the amplifier transistor is a multi-finger transistor;

FIG. 10 illustrates another example of the configuration of the bias circuit when the amplifier transistor is a multi-finger transistor;

FIG. 11 illustrates another example of the configuration of the bias circuit;

FIG. 12 illustrates another example of the configuration of the bias circuit;

FIG. 13 illustrates another example of the configuration of the bias circuit when the amplifier transistor is a multi-finger transistor;

FIG. 14 illustrates another example of the configuration of the bias circuit; and

FIG. 15 illustrates another example of the configuration of the bias circuit.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below with reference to the accompanying drawings. FIG. 1 illustrates an example of the configuration of a transmitting unit 100 that includes a power amplifier module 113, which is an embodiment of the present disclosure. The transmitting unit 100 is used for transmitting various signals, such as audio and data signals, to a base station, in a mobile communication device, such as a cellular phone. The transmitting unit 100 supports multiple radio frequency (RF) bands (multiband). The mobile communication device also includes a receiving unit for receiving signals from a base station. However, an explanation of the receiving unit will be omitted.

As shown in FIG. 1, the transmitting unit 100 includes a baseband section 110, an RF section 111, a power supply circuit 112, a power amplifier module 113, a front-end section 114, and an antenna 115.

The baseband section 110 modulates an input signal, such as an audio signal or a data signal, on the basis of a modulation method, such as HSUPA or LTE, and outputs a modulation signal. In this embodiment, a modulation signal output from the baseband section 110 is an IQ signal (I (In-phase) signal and Q (Quadrature) signal) representing the amplitude and the phase on an IQ plane. The frequency of an IQ signal is, for example, about several MHz to several tens of MHz.

The baseband section 110 also outputs a mode signal MODE which specifies an operation mode of the power amplifier module 113. In this embodiment, the power amplifier module 113 is operable in the envelope tracking (ET) mode and the average power tracking (APT) mode. If the output of the power amplifier module 113 is a predetermined level or higher, the baseband section 110 outputs a mode signal MODE which specifies the ET mode. If the output of the power amplifier module 113 is lower than the predetermined level, the baseband section 110 outputs a mode signal MODE which specifies the APT mode.

The baseband section 110 also outputs a control signal for controlling the power supply voltage in accordance with the operation mode of the power amplifier module 113. More specifically, in the case of the ET mode, the baseband section 110 detects the amplitude level of a modulation signal on the basis of the IQ signal, and outputs a power supply control signal CTRL_(ET) to the power supply circuit 112 so that a power supply voltage V_(REG) to be supplied to the power amplifier module 113 will be at a level corresponding to the amplitude level of an RF signal. On the other hand, in the case of the APT mode, the baseband section 110 outputs a power supply control signal CTRL_(APT) to the power supply circuit 112 so that a power supply voltage V_(REG) to be supplied to the power amplifier module 113 will be at a level corresponding to the average power of the power amplifier module 113.

The RF section 111 generates an RF signal (RF_(IN)) used for performing radio transmission from the IQ signal output from the baseband section 110. The frequency of the RF signal is about several hundreds of MHz to several GHz. In this case, instead of performing direct conversion from the IQ signal into the RF signal, the RF section 111 may first convert the IQ signal into an IF (Intermediate Frequency) signal and then convert the IF signal into the RF signal.

The power supply circuit 112 generates a power supply voltage V_(REG) at a level corresponding to the operation mode, on the basis of the mode signal MODE and the power supply control signal CTRL_(ET) or CTRL_(APT), and supplies the generated power supply voltage V_(REG) to the power amplifier module 113. More specifically, in the case of the ET mode, the power supply circuit 112 generates a power supply voltage V_(REG) (first power supply voltage) corresponding to the power supply control signal CTRL_(ET). In the case of the APT mode, the power supply circuit 112 generates a power supply voltage V_(REG) (second power supply voltage) corresponding to the power supply control signal CTRL_(APT). The power supply circuit 112 may include a DC-to-DC converter which generates a power supply voltage V_(REG) at a desired level from an input voltage (for example, a battery voltage V_(BAT)).

The power amplifier module 113 amplifies power of the RF signal (RF_(IN)) output from the RF section 111 to a level which is high enough to be transmitted to a base station, on the basis of the power supply voltage V_(REG) supplied from the power supply circuit 112, and outputs an amplified signal (RF_(OUT)).

The front-end section 114 performs filtering on the amplified signal (RF_(OUT)) and switching between the amplified signal (RF_(OUT)) and a signal received from a base station. The amplified signal output from the front-end section 114 is transmitted to the base station via the antenna 115.

FIG. 2 illustrates an example of the configuration of the power amplifier module 113. As shown in FIG. 2, the power amplifier module 113 includes transistors 200 _(A) and 200 _(B), bias circuits 210 _(A) and 210 _(B), matching circuits 220, 221, and 222, inductors 230 _(A) and 230 _(B), and a bias control circuit 240.

The transistors 200 _(A) and 200 _(B) form a two-stage amplifier, which amplifies an input RF signal (RF_(IN)) and outputs an amplified signal (RF_(OUT)). The transistors 200 _(A) and 200 _(B) are each constituted by a bipolar transistor, for example, a heterojunction bipolar transistor (HBT). The first-stage (driving-stage) transistor 200 _(A) amplifies the input RF signal (RF_(IN)) and outputs the amplified signal. The second-stage transistor 200 _(B) amplifies the signal output from the transistor 200 _(A) and outputs the amplified signal. The number of stages of the amplifier is not restricted to two, and may be one or three or more.

The bias circuits 210 _(A) and 210 _(B) supply bias to the transistors 200 _(A) and 200 _(B), respectively. The bias circuit 210 _(A) supplies a bias current I_(BIAS1) corresponding to a bias control signal S_(C1) output from the bias control circuit 240 to the transistor 200 _(A). The bias circuit 210 _(B) supplies a bias current I_(BIAS2) corresponding to a bias control signal S_(C2) output from the bias control circuit 240 to the transistor 200 _(B).

The matching circuits 220, 221, and 222 are disposed for performing impedance matching between circuits. The matching circuits 220, 221, and 222 are each constituted by, for example, inductors and capacitors.

The inductors 230 _(A) and 230 _(B) are disposed for the isolation of the RF signal. The power supply voltage V_(REG) is supplied to the transistors 200 _(A) and 200 _(B) via the inductors 230 _(A) and 230 _(B), respectively. In the power amplifier module 113 shown in FIG. 2, the power supply voltage V_(REG) is supplied to both of the transistors 200 _(A) and 200 _(B). However, the power supply voltage V_(REG) may be supplied to only one of the transistors 200 _(A) and 200 _(B), and a power supply voltage of a predetermined level, for example, the battery voltage V_(BAT), may be supplied to the other one of the transistors 200 _(A) and 200 _(B).

The bias control circuit 240 outputs the bias control signals S_(C1) and S_(C2) to the transistors 200 _(A) and 200 _(B), respectively, on the basis of the mode signal MODE so that bias to be supplied to the transistors 200 _(A) and 200 _(B) will be at a suitable level corresponding to the operation mode (ET/APT mode). The control operation using the bias control signals S_(C1) and S_(C2) will be discussed later. The bias control circuit 240 may be disposed outside of the power amplifier module 113.

FIG. 3 illustrates an example of the configuration of the bias circuits 210 _(A) and 210 _(B). A bias circuit 210 _(A1) includes transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ (first and second transistors) and resistors 310 _(A) _(_) ₁, 310 _(A) _(_) ₂, 312 _(A) _(_) ₁ (first resistor), and 312 _(A) _(_) ₂ (second resistor). As shown in FIG. 3, the bias control signal S_(C1) output from the bias control circuit 240 includes bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂ (first and second bias control voltages), and the bias control signal S_(C2) output from the bias control circuit 240 includes bias control voltages V_(C2) _(_) ₁ and V_(C2) _(_) ₂.

The transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ are bipolar transistors, for example, HBTs. The bias control voltage V_(C1) _(_) ₁ is supplied to the base of the transistor 300 _(A) _(_) ₁ via the resistor 310 _(A) _(_) ₁. The bias control voltage V_(C1) _(_) ₂ is supplied to the base of the transistor 300 _(A) _(_) ₂ via the resistor 310 _(A) _(_) ₂. A power supply voltage of a predetermined level, for example the battery voltage V_(BAT), is supplied to the collectors of the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂. One end of the resistor 312 _(A) _(_) ₁ is connected to the emitter of the transistor 300 _(A) _(_) ₁ and the other end thereof is connected to the base of the transistor 200 _(A). That is, the resistor 312 _(A) _(_) ₁ is connected in series with the transistor 300 _(A) _(_) ₁. One end of the resistor 312 _(A) _(_) ₂ is connected to the emitter of the transistor 300 _(A) _(_) ₂ and the other end thereof is connected to the base of the transistor 200 _(A). That is, the resistor 312 _(A) _(_) ₂ is connected in series with the transistor 300 _(A) _(_) ₂. The resistance value R_(B1) _(_) ₁ of the resistor 312 _(A) _(_) ₁ is different from the resistance value R_(B1) _(_) ₂ of the resistor 314 _(A) _(_) ₂.

In the bias circuit 210 _(A1), one of the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ is turned ON under the control of the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂. Then, the bias current I_(BIAS1) is output via one of the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ that is turned ON and the resistor 312 _(A) _(_) ₁ or 312 _(A) _(_) ₂ connected in series with this transistor. This control operation will be described below more specifically. For example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 300 _(A) _(_) ₁ is turned ON and the transistor 300 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A1) outputs the bias current I_(BIAS1) determined by the bias control voltage V_(C1) _(_) ₁ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 300 _(A) _(_) ₁ is turned OFF and the transistor 300 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A1) outputs the bias current I_(BIAS1) determined by the bias control voltage V_(C1) _(_) ₂ and the resistance value R_(B1) _(_) ₂.

The configuration of the bias circuit 210 _(B1) is similar to that of the bias circuit 210 _(A1). Elements of the bias circuit 210 _(B1) equivalent to those of the bias circuit 210 _(A1) are designated by like reference numerals, and an explanation thereof will be omitted. In the bias circuit 210 _(B1), as well as in the bias circuit 210 _(A1), the resistance value R_(B2) _(_) ₁ of the resistor 312 _(B) _(_) ₁ is different from the resistance value R_(B2) _(_) ₂ of the resistor 312 _(B) _(_) ₂.

In the bias circuit 210 _(B1), for example, when the bias control voltage V_(C2) _(_) ₁ is at a high level and the bias control voltage V_(C2) _(_) ₂ is at a low level, the transistor 300 _(B) _(_) ₁ is turned ON and the transistor 300 _(B) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(B1) outputs the bias current I_(BIAS2) determined by the bias control voltage V_(C2) _(_) ₁ and the resistance value R_(B2) _(_) ₁. When the bias control voltage V_(C2) _(_) ₁ is at a low level and the bias control voltage V_(C2) _(_) ₂ is at a high level, the transistor 300 _(B) _(_) ₁ is turned OFF and the transistor 300 _(B) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(B1) outputs the bias current I_(BIAS2) determined by the bias control voltage V_(C2) _(_) ₂ and the resistance value R_(B2) _(_) ₂.

In the power amplifier module 113, in the case of the ET mode, the bias control voltages V_(C1) _(_) ₁ and V_(C2) _(_) ₁ are made to have a high level, while the bias control voltages V_(C1) _(_) ₂ and V_(C2) _(_) ₂ are made to have a low level. In contrast, in the case of the APT mode, the bias control voltages V_(C1) _(_) ₁ and V_(C2) _(_) ₁ are made to have a low level, while the bias control voltages V_(C1) _(_) ₂ and V_(C2) _(_) ₂ are made to have a high level. With this control operation, the power amplifier module 113 is able to generate a bias current based on a suitable bias control voltage and a suitable resistance value corresponding to the operation mode. The value of the bias control voltage V_(C1) _(_) ₁ at a high level may be different from that of the bias control voltage V_(C1) _(_) ₂. For example, the bias control voltage V_(C1) _(_) ₁ at a high level (for example, about 2.85 V) may be higher than the bias control voltage V_(C1) _(_) ₂ at a high level (for example, about 2.8 V). The relationship between the bias control voltages V_(C2) _(_) ₁ and V_(C2) _(_) ₂ may be similar to that between the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂.

FIG. 4A is a graph illustrating an example of the relationship between the output level (dBm) and the power-added efficiency (%) when the power amplifier module 113 is operating in the ET mode. FIG. 4A shows a change in the power-added efficiency in accordance with the magnitudes of the bias control voltage V_(C) (such as V_(C1) _(_) ₁ and V_(C1) _(_) ₂) and the resistance value R_(B) (such as R_(B1) _(_) ₁ and R_(B1) _(_) ₂). In the ET mode, it is desirable to enhance the power-added efficiency. It is thus necessary to determine the bias control voltage V_(C) and the resistance value R_(B) so as to increase the power-added efficiency.

FIG. 4B is a graph illustrating an example of the relationship between the output level (dBm) and the gain (dB) when the power amplifier module 113 is operating in the APT mode. FIG. 4B shows a change in the gain in accordance with the magnitudes of the bias control voltage V_(C) (such as V_(C1) _(_) ₁ and V_(C1) _(_) ₂) and the resistance value R_(B) (such as R_(B1) _(_) ₁ and R_(B1) _(_) ₂). In the APT mode, it is desirable to enhance the linearity. It is thus necessary to determine the bias control voltage V_(C) and the resistance value R_(B) so as to obtain high linearity.

As shown in FIGS. 4A and 4B, the reference to be used for determining the bias control voltage V_(C) and the resistance value R_(B) in the case of the ET mode is different from that in the case of the APT mode. Accordingly, the bias control voltage V_(C) and the resistance value R_(B) suitable for one of the ET mode and the APT mode are not necessarily the same as the bias control voltage V_(C) and the resistance value R_(B) suitable for the other mode. In terms of this point, in the power amplifier module 113, in each of the bias circuits 210 _(A1) and 210 _(B1), the suitable bias control voltage V_(C) (for example, V_(C1) _(_) ₁ or V_(C1) _(_) ₂) and the suitable resistance value R_(B) (for example, R_(B1) _(_) ₁ or R_(B1) _(_) ₂) can be selected in accordance with the operation mode. In this manner, in a power amplifier module which is operable in multiple operation modes, it is possible to control bias to be supplied to an amplifier transistor.

FIG. 5 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A2)) when the amplifier transistor 200 _(A) is a multi-finger transistor. Elements equivalent to those of the bias circuit 210 _(A1) are designated by like reference numerals, and an explanation thereof will be omitted. When the amplifier transistor 200 _(B) is a multi-finger transistor, the bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

In the example shown in FIG. 5, the transistor 200 _(A) is constituted by N unit transistors (fingers) 200 _(A) _(_) ₁ through 200 _(A) _(_) _(N) connected in parallel with each other. The bias circuit 210 _(A2) includes the same number of pairs of transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ (that is, transistors 300 _(A) _(_) ₁ _(_) ₁ through 300 _(A) _(_) ₁ _(_) _(N) and transistors 300 _(A) _(_) ₂ _(_) ₁ through 300 _(A) _(_) ₂ _(_) _(N), respectively) and the same number of pairs of resistors 312 _(A) _(_) ₁ and 312 _(A) _(_) ₂ (that is, resistors 312 _(A) _(_) ₁ _(_) ₁ through 312 _(A) _(_) ₁ _(_) _(N) and resistors 312 _(A) _(_) ₂ _(_) ₁ through 312 _(A) _(_) ₂ _(_) _(N), respectively), which are provided in the bias circuit 210 _(A1), as the number (N) of fingers.

In the bias circuit 210 _(A2), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistors 300 _(A) _(_) ₁ _(_) ₁ through 300 _(A) _(_) ₁ _(_) _(N) are turned ON and the transistors 300 _(A) _(_) ₂ _(_) ₁ through 300 _(A) _(_) ₂ _(_) _(N) are turned OFF. In this case, the bias circuit 210 _(A2) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₁ and the resistance value R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistors 300 _(A) _(_) ₁ _(_) ₁ through 300 _(A) _(_) ₁ _(_) _(N) are turned OFF and the transistors 300 _(A) _(_) ₂ _(_) ₁ through 300 _(A) _(_) ₂ _(_) _(N) are turned ON. In this case, the bias circuit 210 _(A2) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₂ and the resistance value R_(B1) _(_) ₂ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 6 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A3)) when the amplifier transistor 200 _(A) is a multi-finger transistor. Elements equivalent to those of the bias circuits 210 _(A1) and 210 _(A2) are designated by like reference numerals, and an explanation thereof will be omitted. When the amplifier transistor 200 _(B) is a multi-finger transistor, the bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A3) shown in FIG. 6 includes the same number of resistors 312 _(A) _(_) ₁ (that is, 312 _(A) _(_) ₁ _(_) ₁ through 314 _(A) _(_) ₁ _(_) _(N)), which are provided in the bias circuit 210 _(A1), as the number (N) of fingers.

In the bias circuit 210 _(A3), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 300 _(A) _(_) ₁ is turned ON and the transistor 300 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A3) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₁ and the resistance value R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 300 _(A) _(_) ₁ is turned OFF and the transistor 300 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A3) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₂ and the resistance values R_(B1) _(_) ₂ and R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 7 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A4)). Elements equivalent to those of the bias circuit 210 _(A1) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

In the example shown in FIG. 7, the bias circuit 210 _(A4) includes N pairs of transistors 300 _(A) _(_) _(k) and resistors 312 _(A) _(_) _(k) (N>2). In accordance with the N pairs of transistors 300 _(A) _(_) _(k) and resistors 312 _(A) _(_) _(k), N bias control voltages (V_(C1) _(_) ₁ through V_(C1) _(_) _(N)) are input from the bias control circuit 240 into the bias circuit 210 _(A4).

In the bias circuit 210 _(A4), for example, when the bias control voltage V_(C1) _(_) _(k) is at a high level and the other bias control voltages are at a low level, among the transistors 300 _(A) _(_) _(n) (n=1 to N), the transistor 300 _(A) _(_) _(k) is turned ON and the other transistors are turned OFF. In this case, the bias circuit 210 _(A4) outputs the bias current I_(BIAS1) determined by the bias control voltage V_(C1) _(_) _(k) and the resistance value R_(B1) _(_) _(k) to the transistor 200 _(A) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 8 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A5)). Elements equivalent to those of the bias circuit 210 _(A1) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A5) shown in FIG. 8 includes transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ (first and second transistors) instead of the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ provided in the bias circuit 210 _(A1). The bias circuit 210 _(A5) also includes a transistor 810 _(A) (third transistor) and a resistor 820 _(A) (third resistor). In addition to the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂ (first and second bias control voltages), a bias control voltage V_(C1) _(_) ₃ (third bias control voltage) is also input from the bias control circuit 240 to the bias circuit 210 _(A5).

The transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ are field-effect transistors (FETs). The bias control voltage V_(C1) _(_) ₁ is supplied to the gate of the transistor 800 _(A) _(_) ₁ via the resistor 310 _(A) _(_) ₁. The bias control voltage V_(C1) _(_) ₂ is supplied to the gate of the transistor 800 _(A) _(_) ₂ via the resistor 310 _(A) _(_) ₂. The drains of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ are connected to the emitter of the transistor 810 _(A). The sources of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ are connected to the resistors 312 _(A) _(_) ₁ and 314 _(A) _(_) ₂, respectively.

The transistor 810 _(A) is a bipolar transistor, for example, an HBT. The bias control voltage V_(C1) _(_) ₃ is supplied to the base of the transistor 810 _(A) via the resistor 820 _(A). A power supply voltage of a predetermined level, for example the battery voltage V_(BAT), is supplied to the collector of the transistor 810 _(A). The emitter of the transistor 810 _(A) is connected to the drains of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂. That is, the transistor 810 _(A) is connected in series with the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂.

In the bias circuit 210 _(A5), one of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ is turned ON under the control of the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂. Additionally, in the bias circuit 210 _(A5), under the control of the bias control voltage V_(C1) _(_) ₃, the currents to be supplied to the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ are controlled. For example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 800 _(A) _(_) ₁ is turned ON and the transistor 800 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A5) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 800 _(A) _(_) ₁ is turned OFF and the transistor 800 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A5) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₂. With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 9 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A6)) when the amplifier transistor 200 _(A) is a multi-finger transistor. Elements equivalent to those of the bias circuits 210 _(A2) and 210 _(A5) are designated by like reference numerals, and an explanation thereof will be omitted. When the amplifier transistor 200 _(B) is a multi-finger transistor, the bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A6) shown in FIG. 9 includes the same number of pairs of transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ (that is, transistors 800 _(A) _(_) ₁ _(_) ₁ through 800 _(A) _(_) ₁ _(_) _(N) and transistors 800 _(A) _(_) ₂ _(_) ₁ through 800 _(A) _(_) ₂ _(_) _(N), respectively) and the same number of pairs of resistors 312 _(A) _(_) ₁ and 312 _(A) _(_) ₂ (that is, resistors 312 _(A) _(_) ₁ _(_) ₁ through 314 _(A) _(_) ₁ _(_) _(N) and resistors 314 _(A) _(_) ₂ _(_) ₁ through 314 _(A) _(_) ₂ _(_) _(N), respectively), which are provided in the bias circuit 210 _(A5), as the number (N) of fingers.

In the bias circuit 210 _(A6), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 800 _(A) _(_) ₁ _(_) _(k) is turned ON and the transistor 800 _(A) _(_) ₂ _(_) _(k) is turned OFF (k=1 to N). In this case, the bias circuit 210 _(A6) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 800 _(A) _(_) ₁ _(_) _(k) is turned OFF and the transistor 800 _(A) _(_) ₂ _(_) _(k) is turned ON (k=1 to N). In this case, the bias circuit 210 _(A6) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₂ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 10 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A7)) when the amplifier transistor 200 _(A) is a multi-finger transistor. Elements equivalent to those of the bias circuits 210 _(A3) and 210 _(A5) are designated by like reference numerals, and an explanation thereof will be omitted. When the amplifier transistor 200 _(B) is a multi-finger transistor, the bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A7) shown in FIG. 10 includes the same number of resistors 312 _(A) _(_) ₁ (that is, 312 _(A) _(_) ₁ _(_) ₁ through 312 _(A) _(_) ₁ _(_) _(N)), which are provided in the bias circuit 210 _(A5), as the number (N) of fingers.

In the bias circuit 210 _(A7), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 800 _(A) _(_) ₁ is turned ON and the transistor 800 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A7) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 800 _(A) _(_) ₁ is turned OFF and the transistor 800 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A7) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance values R_(B1) _(_) ₂ and R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 11 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A8)). Elements equivalent to those of the bias circuit 210 _(A5) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A8) is a modified example of the bias circuit 210 _(A5). In the bias circuit 210 _(A8), resistors 314 _(A) _(_) ₁ and 312 _(A) _(_) ₂ connected in series with each other are connected to the emitter of the transistor 810 _(A). The drain of the transistor 800 _(A) _(_) ₁ is connected to one end of the resistor 312 _(A) _(_) ₂ and the source thereof is connected to the other end of the resistor 312 _(A) _(_) ₂. The drain of the transistor 800 _(A) _(_) ₂ is connected to one end of the resistor 312 _(A) _(_) ₁ and the source thereof is connected to the other end of the resistor 314 _(A) _(_) ₁.

In the bias circuit 210 _(A8), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 800 _(A) _(_) ₁ is turned ON and the transistor 800 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A8) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 800 _(A) _(_) ₁ is turned OFF and the transistor 800 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A8) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₂. With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 12 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A9)). Elements equivalent to those of the bias circuit 210 _(A8) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A9) is a modified example of the bias circuit 210 _(A8). The configuration of the bias circuit 210 _(A9) is the same configuration as the bias circuit 210 _(A8), except that bias circuit 210 _(A9) does not include the resistor 310 _(A) _(_) ₂ and the transistor 800 _(A) _(_) ₂ provided in the bias circuit 210 _(A8).

In the bias circuit 210 _(A9), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level, the transistor 800 _(A) _(_) ₁ is turned ON. In this case, the bias circuit 210 _(A9) outputs the bias current I_(BIAS1) determined by the bias control voltage V_(C1) _(_) ₁ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level, the transistor 800 _(A) _(_) ₁ is turned OFF. In this case, the bias circuit 210 _(A9) outputs the bias current I_(BIAS1) determined by the bias control voltage V_(C1) _(_) ₃ and the resistance values R_(B1) _(_) ₁ and R_(B1) _(_) ₂. With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A) _(_) ₁.

FIG. 13 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A10)) when the amplifier transistor 200 _(A) is a multi-finger transistor. Elements equivalent to those of the bias circuits 210 _(A7) and 210 _(A9) are designated by like reference numerals, and an explanation thereof will be omitted. When the amplifier transistor 200 _(B) is a multi-finger transistor, the bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A10) shown in FIG. 13 includes the same number of resistors 312 _(A) _(_) ₁ (that is, 312 _(A) _(_) ₁ _(_) ₁ through 314 _(A) _(_) ₁ _(_) _(N)), the resistor 312 _(A) _(_) ₁ being provided in the bias circuit 210 _(A9), as the number (N) of fingers.

In the bias circuit 210 _(A10), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level, the transistor 800 _(A) _(_) ₁ is turned ON. In this case, the bias circuit 210 _(A10) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₁ and the resistance value R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). When the bias control voltage V_(C1) _(_) ₁ is at a low level, the transistor 800 _(A) _(_) ₁ is turned OFF. In this case, the bias circuit 210 _(A10) outputs the bias current I_(BIAS1) _(_) _(k) determined by the bias control voltage V_(C1) _(_) ₃ and the resistance values R_(B1) _(_) ₂ and R_(B1) _(_) ₁ _(_) _(k) to the transistor 200 _(A) _(_) _(k) (k=1 to N). With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A) _(_) ₁.

FIG. 14 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A) _(_) ₁ _(_) ₁). Elements equivalent to those of the bias circuits 210 _(A1) and 210 _(A5) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A) _(_) ₁ _(_) ₁ shown in FIG. 14 includes transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ instead of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ provided in the bias circuit 210 _(A5).

The collector of the transistor 300 _(A) _(_) ₁ is connected to the emitter of the transistor 810 _(A) via the resistor 312 _(A) _(_) ₁, and the emitter thereof is connected to the transistor 200 _(A). The collector of the transistor 300 _(A) _(_) ₂ is connected to the emitter of the transistor 810 _(A) via the resistor 312 _(A) _(_) ₂, and the emitter thereof is connected to the transistor 200 _(A).

In the bias circuit 210 _(A) _(_) ₁ _(_) ₁, one of the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ is turned ON under the control of the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂. Additionally, in the bias circuit 210 _(A) _(_) ₁ _(_) ₁, under the control of the bias control voltage V_(C1) _(_) ₂, the currents to be supplied to the transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ are controlled. For example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 300 _(A) _(_) ₁ is turned ON and the transistor 300 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A) _(_) ₁ _(_) ₁ outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 300 _(A) _(_) ₁ is turned OFF and the transistor 300 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A11) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₂. With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

FIG. 15 illustrates an example of the configuration of the bias circuit 210 _(A) (210 _(A12)). Elements equivalent to those of the bias circuit 210 _(A8) are designated by like reference numerals, and an explanation thereof will be omitted. The bias circuit 210 _(B) may be configured similarly to the bias circuit 210 _(A).

The bias circuit 210 _(A12) is a modified example of the bias circuit 210 _(A8). The bias circuit 210 _(A12) includes transistors 300 _(A) _(_) ₁ and 300 _(A) _(_) ₂ instead of the transistors 800 _(A) _(_) ₁ and 800 _(A) _(_) ₂ provided in the bias circuit 210 _(A8). The collector of the transistor 300 _(A) _(_) ₁ is connected to one end of the resistor 312 _(A) _(_) ₂ and the emitter thereof is connected to the other end of the resistor 312 _(A) _(_) ₂. The collector of the transistor 300 _(A) _(_) ₂ is connected to one end of the resistor 312 _(A) _(_) ₁ and the emitter thereof is connected to the other end of the resistor 312 _(A) _(_) ₁.

In the bias circuit 210 _(A12), for example, when the bias control voltage V_(C1) _(_) ₁ is at a high level and the bias control voltage V_(C1) _(_) ₂ is at a low level, the transistor 300 _(A) _(_) ₁ is turned ON and the transistor 300 _(A) _(_) ₂ is turned OFF. In this case, the bias circuit 210 _(A12) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₁. When the bias control voltage V_(C1) _(_) ₁ is at a low level and the bias control voltage V_(C1) _(_) ₂ is at a high level, the transistor 300 _(A) _(_) ₁ is turned OFF and the transistor 300 _(A) _(_) ₂ is turned ON. In this case, the bias circuit 210 _(A12) outputs the bias current I_(BIAS1) determined by the bias control voltages V_(C1) _(_) ₂ and V_(C1) _(_) ₃ and the resistance value R_(B1) _(_) ₂. With this configuration, it is possible to obtain advantages similar to those achieved by the bias circuit 210 _(A1).

An exemplary embodiment of the disclosure has been discussed above. In the power amplifier module 113 including one of the bias circuits 210A₁ through 210A₈, 210A₁₁, and 210A₁₂, the ON state and the OFF state of two transistors are complementarily switched under the control of the bias control voltage V_(C1) _(_) ₁ supplied in a first operation mode (for example, the ET mode) and the bias control voltage V_(C1) _(_) ₂ supplied in a second operation mode (for example, the APT mode). Accordingly, the power amplifier module 113 is able to generate a bias current determined by the corresponding bias control voltage and resistance value based on the operation mode. It is thus possible to suitably control bias to be supplied to an amplifier transistor in a power amplifier module that is operable in multiple operation modes.

In the power amplifier module 113 including one of the bias circuits 210A₅ through 210A₈, 210A₁₁, and 210A₁₂, the ON state and the OFF state of two transistors are complementarily switched under the control of the bias control voltages V_(C1) _(_) ₁ and V_(C1) _(_) ₂, and also, the currents supplied to these transistors are controlled by using the bias control voltage V_(C1) _(_) ₃. Accordingly, the power amplifier module 113 is able to generate a bias current determined by the corresponding bias control voltages and resistance value based on the operation mode. It is thus possible to suitably control bias to be supplied to an amplifier transistor in a power amplifier module that is operable in multiple operation modes.

In the power amplifier module 113 including one of the bias circuits 210A₉ and 210A₁₀, the ON state and the OFF state of a transistor are switched under the control of the bias control voltage V_(C1) _(_) ₁ supplied in the first operation mode (for example, the ET mode), and also, the current supplied to this transistor is controlled by using the bias control voltage V_(C1) _(_) ₃. Accordingly, the power amplifier module 113 is able to generate a bias current determined by the corresponding bias control voltage and resistance value based on the operation mode. It is thus possible to suitably control bias to be supplied to an amplifier transistor in a power amplifier module that is operable in multiple operation modes.

The embodiment described above is provided for facilitating the understanding of the invention, but is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Modifications and/or improvements may be made to the invention without departing from the scope and spirit of the invention, and equivalents of the invention are also encompassed in the invention. That is, suitable design changes made to the embodiment by those skilled in the art are also encompassed in the invention as long as they are within the scope and spirit of the invention. For example, the elements of the embodiment and the positions, materials, conditions, configurations, and sizes thereof are not restricted to those described in the embodiment and may be changed in an appropriate manner. The elements of the embodiment may be combined as long as such combinations are technically possible, and configurations obtained by combining the elements of the embodiment are also encompassed in the invention as long as they are within the scope and spirit of the invention.

While embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims. 

1. A power amplifier module comprising: an amplifier transistor having a plurality of fingers and to which a first power supply voltage or a second power supply voltage is supplied based on a mode signal supplied to the power amplifier module, the amplifier transistor receiving a first signal and outputting a second signal obtained by amplifying the first signal; and a bias circuit that supplies a bias current to the amplifier transistor, the bias circuit including: a plurality of bias transistors connected in parallel, each of the plurality of bias transistors being turned ON by a bias control voltage based on a mode signal indicating an operation mode to be used to amplify the first signal; a first resistor; a common node, wherein the first resistor is connected at a first end to an emitter of a first of the plurality of bias transistors and at a second end to the common node, and wherein an emitter of a second of the plurality of bias transistors is connected to the common node; and a plurality of resistors, wherein each one of the plurality of resistors is connected at a first end to the common node and at a second end to a respective one of the plurality of fingers of the amplifier transistor.
 2. The power amplifier module of claim 1, wherein the first of the plurality of bias transistors is turned ON by a first bias control voltage which is supplied when the mode signal indicates that a first operation mode is to be used to amplify the first signal and the second of the plurality of bias transistors is turned ON by a second bias control voltage which is supplied when the mode signal indicates that a second operation mode is to be used to amplify the first signal.
 3. The power amplifier module of claim 2, wherein the first operation mode is a high power mode and the second operation mode is a low power mode.
 4. The power amplifier module of claim 2, wherein the first operation mode is an envelope tracking (ET) mode and the second operation mode is an average power tracking (APT) mode.
 5. The power amplifier module according to claim 3, wherein the first bias control voltage is greater than the second bias control voltage.
 6. The power amplifier module according to claim 4, wherein the first bias control voltage is greater than the second bias control voltage.
 7. A multi-stage power amplifier module, each stage of a plurality of amplification stages comprising: an amplifier transistor having a plurality of fingers and to which a first power supply voltage or a second power supply voltage is supplied based on a mode signal supplied to the power amplifier module, the amplifier transistor receiving a first signal and outputting a second signal obtained by amplifying the first signal; and a bias circuit that supplies a bias current to the amplifier transistor, the bias circuit including: a first resistor, a first bias transistor that is connected in series with the first resistor, a second resistor, a second bias transistor that is connected in series with the second resistor, and a common node, wherein the first resistor is connected at a first end to an emitter of the first bias transistors and at a second end to the common node, and the second resistor is connected at a first end to an emitter of the second bias transistor and at a second end to the common node.
 8. The power amplifier module of claim 7, wherein, for each stage, the first bias transistor is turned ON by a first bias control voltage which is supplied when the mode signal indicates that a first operation mode is to be used to amplify the first signal and the second bias transistor is turned ON by a second bias control voltage which is supplied when the mode signal indicates that a second operation mode is to be used to amplify the first signal.
 9. The power amplifier module of claim 8, wherein, for each stage, the first operation mode is a high power mode and the second operation mode is a low power mode.
 10. The power amplifier module of claim 8, wherein, for each stage, the first operation mode is an envelope tracking (ET) mode and the second operation mode is an average power tracking (APT) mode.
 11. A multi-stage power amplifier module, each stage of a plurality of amplification stages comprising: an amplifier transistor having a plurality of fingers and to which a first power supply voltage or a second power supply voltage is supplied based on a mode signal supplied to the power amplifier module, the amplifier transistor receiving a first signal and outputting a second signal obtained by amplifying the first signal; and a bias circuit that supplies a bias current to the amplifier transistor, the bias circuit including: a plurality of bias transistors connected in parallel, each of the plurality of bias transistors being turned ON by a bias control voltage based on a mode signal indicating an operation mode to be used to amplify the first signal; a first resistor; a common node, wherein the first resistor is connected at a first end to an emitter of a first of the plurality of bias transistors and at a second end to the common node, and wherein an emitter of a second of the plurality of bias transistors is connected to the common node; and a plurality of resistors, wherein each one of the plurality of resistors is connected at a first end to the common node and at a second end to a respective one of the plurality of fingers of the amplifier transistor.
 12. The power amplifier module of claim 11, wherein, for each stage, the first of the plurality of bias transistors is turned ON by a first bias control voltage which is supplied when the mode signal indicates that a first operation mode is to be used to amplify the first signal and the second of the plurality of bias transistors is turned ON by a second bias control voltage which is supplied when the mode signal indicates that a second operation mode is to be used to amplify the first signal.
 13. The power amplifier module of claim 12, wherein, for each stage, the first operation mode is a high power mode and the second operation mode is a low power mode.
 14. The power amplifier module of claim 12, wherein, for each stage, the first operation mode is an envelope tracking (ET) mode and the second operation mode is an average power tracking (APT) mode.
 15. A multi-stage power amplifier module, each stage of a plurality of amplification stages comprising: an amplifier transistor having a plurality of fingers and to which a first power supply voltage or a second power supply voltage is supplied based on a mode signal supplied to the power amplifier module, the amplifier transistor receiving a first signal and outputting a second signal obtained by amplifying the first signal; and a first stage comprising: a first bias circuit that supplies a bias current to the amplifier transistor, the first bias circuit including: a first resistor, a first bias transistor that is connected in series with the first resistor, a second resistor, and a second bias transistor that is connected in series with the second resistor; and a second stage comprising: a second bias circuit that supplies a bias current to the amplifier transistor, the second bias circuit including: a plurality of bias transistors connected in parallel, each of the plurality of bias transistors being turned ON by a bias control voltage based on a mode signal indicating an operation mode to be used to amplify the first signal; a first resistor; a common node, wherein the first resistor is connected at a first end to an emitter of a first of the plurality of bias transistors and at a second end to the common node, and wherein an emitter of a second of the plurality of bias transistors is connected to the common node; and a second plurality of resistors, wherein each one of the second plurality of resistors is connected at a first end to the common node and at a second end to a respective one of the plurality of fingers of the amplifier transistor.
 16. The power amplifier module of claim 9, wherein, for each stage, the first of the plurality of bias transistors is turned ON by a first bias control voltage which is supplied when the mode signal indicates that a first operation mode is to be used to amplify the first signal and the second of the plurality of bias transistors is turned ON by a second bias control voltage which is supplied when the mode signal indicates that a second operation mode is to be used to amplify the first signal.
 17. The power amplifier module of claim 16, wherein, for each stage, the first operation mode is a high power mode and the second operation mode is a low power mode.
 18. The power amplifier module of claim 16, wherein, for each stage, the first operation mode is an envelope tracking (ET) mode and the second operation mode is an average power tracking (APT) mode. 